1. Field of the Invention:
The present invention relates to an inverter used for driving a backlight of a liquid crystal display (LCD). More particularly, the present invention relates to a balance coil and an inverter for driving a plurality of Cold Cathode Fluorescent Lamps (CCFL) in parallel.
2. Description of the Related Art:
Current LCD displays require a backlight unit that is small in size and efficient. Consequently, CCFL is widely used as a light source of backlight unit. However, a single back light unit equipped with only one lamp is not sufficient for use in a wide-bodied display. Instead, multiple backlight units using a plurality of lamps are used because they better satisfy the requirements of a wide-bodied display.
In order to minimize cost and simplify structure, multiple backlight units drive the plurality of lamps in parallel. A conventional parallel driving circuit utilizes a balance coil for balancing currents in each lamp.
FIG. 1 is a schematic representation illustrating an inverter for driving a multiple backlight disposed with a balance coil, and FIG. 2 is a schematic representation illustrating a structure of a conventional balance coil.
Referring to FIGS. 1 and 2, an inverter includes a driving circuit 1, a transformer 2 for driving two fluorescent lamps LP1 and LP2, and a feedback control circuit 3.
Furthermore, the inverter includes balance coils 4 and 4′, respectively, connected to a lamp for balancing current flowing through a first lamp LP1 and a second lamp LP2. Ballast capacitors C1 and C2 are used for preventing the current flowing through each lamp LP1 and LP2 from increasing, and are connected in series to each lamp LP1 and LP2.
Referring to FIG. 2, the balance coils 4 and 4′ include a bobbin 11, a core 12 inserted into a groove 11a of the bobbin 11 and a coil 13 wrapped at an external side of the bobbin 11.
The current flowing through each lamp LP1 and LP2 is balanced between each lamp by the coils 4 and 4′. Thereby, the backlight unit is stably maintained without any luminance difference between the lamps.
However, in the conventional inverter, one balance coil 4 and ‘4’ is connected to each lamp LP1 and LP2, thus requiring a large number of balance coils. Therefore, because of the large number of balance coils used the conventional inverter is uneconomical and is large in size.
Furthermore, the conventional inverter uses ballast capacitors C1 and C2 to prevent a current increase in each lamp, and if the ballast capacitors are used, a high voltage is applied to both ends of the transformer 2 to the detriment of the transformer. Consequently, the use of ballast capacitors reduces the stability of the transformer.
Meanwhile, the conventional balance coils 4 and 4′ have a limitation in that by structurally increasing the size of the core 12 there is a high possibility of creating an inferior quality of goods due to core saturation.
Accordingly, there is a need for an improved inverter used for driving a backlight of a liquid crystal display (LCD) that is both small in size and economical.